abstract class in Kotlin

In Kotlin, abstract class is declared using the abstract keyword in front of class. An abstract class can not instantiated means we can not create object for the abstract class.
* We can’t create an object for abstract class.
* An abstract class can contain both abstract and non-abstract members
* All the variables (properties) and member functions of an abstract class are by default non-abstract. So, if we want to override these members in the child class then we need to use open keyword.
* If we declare a member function as abstract then we does not need to annotate with open keyword because these are open by default.
* An abstract member function doesn’t have a body, and it must be implemented in the derived class.

```
abstract class Employee(val name: String,val experience: Int) {   
    abstract var salary: Double
    abstract var date: String
    abstract fun dateOfBirth(date:String)
  
    fun employeeDetails() {
        println("Name of the employee: $name")
        println("Experience in years: $experience")
        println("Annual Salary: $salary")
        println("Birth date: $date")
    }
}

class Engineer(name: String, experience: Int) : Employee(name,experience) {
    override var salary = 500000.00
    override var date = ""
    override fun dateOfBirth(date:String){
        this.date = date;
    }
}

fun main() {
    val eng = Engineer("Tom",2)
    eng.dateOfBirth("02 December 1994")
    eng.employeeDetails()
}
```
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